P. S. Kumar, G. D. K. Kumar, S. Baskaran
SHORT COMMUNICATION
(m, 2 H), 3.61–3.59 (m, 1 H), 3.3 (br. s, 1 H), 2.65–2.62 (m, 1 H),
2.59–2.50 (m, 1 H), 2.38–2.36 (m, 1 H), 2.20–2.18 (m, 1 H) ppm.
13C NMR (100 MHz, CDCl3): δ = 177.14, 78.8, 65.6, 61.9, 28.0,
24.5 ppm. HRMS (ESI): calcd. for C6H9N3O3Na [M + Na]+
194.0542; found 194.0546.
Supporting Information (see footnote on the first page of this arti-
cle): Experimental procedures and full spectroscopic data.
Acknowledgments
This work was financially supported by the Council of Scientific
and Industrial Research (CSIR), New Delhi. The authors thank
the Department of Science & Technology (DST), New Delhi, for
NMR and HRTEM facilities. P. S. K thanks the Council of Scien-
tific and Industrial Research (CSIR), New Delhi, for a research
fellowship.
Figure 2. ORTEP diagram of 2-epi-4-deoxyfagomine (41).
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also been found to be an important intermediate in the
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Scheme 4. Synthesis of (5S,6S)-5-hydroxy-6-(hydroxymethyl)piper-
idin-2-one (42).
Conclusions
We developed a simple and an efficient method for the
chemoselective cleavage of benzylidene acetal and 2-phenyl-
1,3-oxazolidine by using PMA/SiO2 (0.5 mol-%) as a cata-
lyst under heterogeneous conditions. The remarkable fea-
tures of our method are mild and clean reaction conditions,
simplicity in operation even on large scale and, finally, the
active catalyst can be readily recovered and recycled with-
out any loss of activity. The chemoselective nature of the
PMA/SiO2 reagent system was exploited in the stereoselec-
tive synthesis of 2-epi-4-deoxyfagomine and its analogues.
We believe that this truly catalytic method for the selective
deprotection of benzylidene acetal will find practical appli-
cation in organic synthesis.
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Experimental Section
General Procedure: A mixture of benzylidene acetal 13 (2 g,
6.56 mmol) and PMA/SiO2 (740 mg, 0.0327 mmol based on PMA)
in DCM (25 mL) was stirred at room temperature for 4 h. After
completion of the reaction, as indicated by TLC, the reaction mix-
ture was filtered to recover the catalyst and the filtrate was concen-
trated under reduced pressure. The crude product was purified by
column chromatography (silica gel; 30–50% EtOAc in hexane) to
give the corresponding chiral lactone 14 in good yield (0.998 g,
89%). Physical data for 14: [α]2D6 = +49.8 (c = 1, CHCl3). IR (neat):
ν = 3395, 2925, 2100, 1758, 1268, 1182, 1156, 1060, 916, 809 cm–1.
˜
1H NMR (400 MHz, CDCl3): δ = 4.69–4.66 (m, 1 H), 3.87–3.86
6066
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